Visual information entering the brain is constantly changing. Its interpretation depends on the observers' goals, and on cognitive states that also change in response to current and previous visual input. Yet most of our knowledge of vision deals with spatial vision and spatial attention, and most existing computational models of vision and visual attention are static; they deal with stimuli that are isolated in time. This represents a critical barrier to a comprehensive theory of visual perception and attention. Temporal attention is the prioritized processing of a stimulus at a specific point in time, which can be voluntary, when a stimulus time can be anticipated, or involuntary, when attention is triggered automatically by a stimulus. The impact of temporal attention on perception and sensory cortical responses has been little investigated, despite its indispensable role in our understanding of a constantly changing environment. We propose to fill this critical gap in the cognitive neuroscience of attention. Our long-term goal is to develop a spatiotemporal theory of cortical computation, widely applicable in basic and translational research in perceptual and cognitive neuroscience. Our short-term goal is to investigate temporal attention to understand how perception is shaped by dynamic interactions between sensory input and attentional modulation, and how visual cortical processing underlies such interactions. We propose an innovative theoretical framework, which makes explicit how perception and attention interact across time (Aim 1). Two alternative dynamic models, early-gain vs. late-competition, in which temporal attention modulates different stages of processing, will be tested and constrained with data gathered with innovative experimental protocols, combining behavioral (psychophysics; Aim 2) and neuroimaging (magnetoencephalography, MEG; Aim 3) methods. Because orientation processing is well-characterized psychophysically and neurophysiologically in a static setting, we will use orientation discrimination and estimation tasks to determine the dynamic interactions between perception and attention. The empirical results will significantly advance our understanding of the time-course, perceptual consequences, resource limitations, and underlying neural mechanisms of temporal attention, and will also distinguish between alternative models and constrain model parameters. By integrating theory with behavioral and neuroimaging data, we will characterize how temporal attention dynamically changes perception and neural responses. The proposed research is fully in line with the NEI mission. It investigates how temporal attention modulates brain processing of visual information and how neural activity relates to visual perception. Further, because dynamic attention allocation is a central function of the visual system, the proposed research in healthy observers will be readily applicable to translational research in special populations, and may advance our understanding of abnormalities in temporal processing and temporal attention that have been associated with personality traits, like impulsivity, and prevalent disorders such as ADHD, autism, visual neglect and dyslexia.